Big Ben chimed for three minutes on Friday to ring in the Olympic Games, which were set to kick off later in the British capital with the much anticipated opening ceremony.
The giant bell, whose clock tower is one of London's best-loved landmarks, was joined by hundreds of churches and bell-ringers across the country in a cacophony to mark the start of the Games.
The bell onboard Queen Elizabeth II's barge, which is carrying the Olympic flame down the Thames as part of its final journey to the Olympic Stadium, also joined in the ringing at 8:12 am (0712 GMT).
The ringing came 12 hours before pre-ceremony entertainment was due to kick off in the stadium at the symbolic time of 8:12 pm, or 20:12.
Organiser Martin Creed, a previous winner of Britain's prestigious Turner Prize for art, encouraged everyone in Britain to join in the "All the Bells" event.
Creed aims to set a world record for the largest number of bells rung simultaneously, and has encouraged people to ring everything from doorbells to bells on their bicycles.
The Royal Navy rang bells on its ships and those at shore bases, while the national parliaments of Scotland, Wales and Northern Ireland also joined in, pealing in unison with Big Ben.
It is believed to be the first time that Big Ben has rung outside its normal schedule since 1952, when it tolled 56 times to mark the death of King George VI, aged 56.
Officials gave special permission for the Westminster bell to break its normal timetable.
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